The ECS uses archetype-based storage with SoA (Structure of Arrays) backends. Components have replication policies — distance-filtered, ownership-filtered, broadcast, or local-only. The system scheduler supports dependency ordering and cadence-based execution. Behavior scripts run in a sandboxed environment with lifecycle hooks (onSpawn, update, onInput, onInteract, onCollide, onTriggerEnter, onTriggerExit, onControlBegin, onControlEnd, onLiquidEnter, onLiquidExit) and use require() for builtins and library modules.

Netcode

Binary wire protocol with dual-channel architecture: a reliable control channel and an unreliable snapshot channel. The engine runs at 60 Hz with a fixed-step ticker. Snapshot replication uses binary-encoded delta compression with 5 frames of redundancy per message — only changed fields are transmitted. Area-of-interest filtering means clients only receive state for nearby entities, with grace periods to prevent oscillation at boundaries. A server-driven dynamic throttle adjusts per-client tick rate based on input buffer health.

Physics

Deterministic WASM physics engine. Server-authoritative with client-side prediction. Character controllers, rigid bodies, colliders, sensor events, and overlap tracking. Raycast API with configurable distance, group masks, and entity filtering. One physics world per place — entity transfers between places dispose and recreate physics state. Client-side prediction uses an operation log buffer per component with mismatch detection and rollback resimulation up to 45 ticks. Interpolation for smooth remote entity rendering.

Asset Pipeline

Everything generates from natural language — 3D models (rigged characters with skeleton and animations, or static props), images, transparent PNGs, pixel art, music, sound effects, and custom voices. Every 3D model goes through automatic post-processing: scale normalization, mesh optimization (20-40% file size reduction), AVIF texture compression, 4-level LOD generation, and convex decomposition for physics colliders. LOD and collider generation run in parallel. Impostor rendering bakes distant models into flat billboards. Users can upload their own assets through the same pipeline.

AI in Games

Three built-in LLM job types for any behavior script: free-form chat with persistent conversation memory, structured JSON generation with schema validation, and memory reset. Savi can become a live dungeon master — behavior scripts send world events (boss defeated, secret found, player choices) and Savi reacts in real-time, modifying the world and spawning encounters. Background agents (wisps) run concurrently for parallel tasks.

Game Feel

52-method Juice API across 13 categories: object effects (highlight, shake, dissolve, trail), camera (screen shake, hitstop, zoom, letterbox), screen effects (flash, vignette, slow-mo), particles, UI (damage numbers, toasts, announcements), spatial audio with 5 buses and reverb zones, timing and schedules, mood and weather, data registries, encounter waves, narrative dialog and choice trees, progress tracking, and economy systems. Audience routing controls who sees each effect.

Places, Terrain, and Mods

Games can have multiple places — dungeons, realms, dimensions — each with their own terrain, physics world, atmosphere, and entities. Heightmap terrain with material blending, rivers, ponds, oceans, and a scatter system for automated object distribution (poisson disk, grid, clustered sampling). Mods are publishable and installable — creators have built a Cinemachine Toolkit, Slash FX Tool, Animation Browser, and Prefab Painter.

What People Build

Any genre: roguelikes, shooters, platformers, RPGs, racing games, puzzle games, horror games, cozy sims, soulslikes, MMOs, TCGs, survival games, idle clickers, bullet hells, fishing simulators. Complete worlds with terrain, buildings, characters, enemies, items, vehicles, music, game logic, atmosphere, AI-powered NPCs, and multi-scene environments. Every game on this page was made with words, not code.

The Team

Founded by Jacob Sansbury (second company; previous exit to Robinhood). Built by a team of under 10 and backed by an unannounced round. Spawn spent about 18 months in early alpha and moved into beta in February 2026. Still early and iterating fast.

What we're building, and every engine release: spawn.co/s

Full technical documentation: spawn.co/llms.txt

© 2026 Sunbelt Computer Software